This invention relates to an electronic watt-hour meter which particularly includes a clock circuit and is capable of transferring the display of the measured amount of electric power in accordance with preset time zones and the like and also in accordance with programs.
An ordinary electronic watt-hour meter of the above described type comprises an electric power measuring device for measuring consumed electric power, a clock circuit for generating a clock signal, a data setting device for setting data such as time zones in a day, holidays and the like, to which different charge rates are applied, a memory circuit for memorizing the data set by the data setting device, a central processing unit (CPU) which is operable to write and read the set data into and out of the memory circuit and to designate, in accordance with the set data, a position where the measured value is to be displayed, and a display device for displaying the measured value at the designated position.
In the above described watt-hour meter, the measured value (in watts) is delivered to CPU in the form of a pulse signal, while the clock circuit constantly supplies a clock signal representing the present instant to CPU. The CPU writes and reads the data set by the setting device into and out of the memory circuit, and the display device has a plurality of displaying positions for displaying the measured amounts of electric power as well as the maximum power demand.
With the above described construction of the conventional watt-hour meter, the data such as the time zones, holidays and the like must be set for every individual watt-hour meter, and therefore a data setting device in the form of a keyboard switch has been ordinarily provided in combination with the watt-hour meter. However, since it is essential to prevent unauthorized alteration of the set values from outside, the keyboard switch must be sealed after the completion of the setting operation, thus requiring a considerable amount of time for setting data, although the keyboard switch has an advantageous feature of a general-use construction. Furthermore, the keyboard switch requires a comparatively large space, rendering impossible to reduce the size of the watt-hour meter. In addition, since a watt-hour meter of two, three or four time zones requires a corresponding number of display positions, it is impossible to convert a watt-hour meter of, for instance, four time zones, to that of five time zones.
In the above described conventional watt-hour meter, the power measuring device is provided with an electric power conversion circuit for converting the measured value (in watts) into a pulse signal corresponding to the measured value, and a frequency-divider for dividing the frequency of the pulse signal at desired rates. The output of the frequency-divider is delivered to the CPU.
For eliminating the above described difficulties, there has been proposed a modification wherein the operation of frequency-divider is programmed such that the pulse rate of the output signal is varied in accordance with the time zones and the like. However, nothing has been proposed about the improvement of the data setting device for eliminating the above described difficulties.